1. Field of the Invention
The present invention relates to power switches, and more particularly to infrared activated power switches.
2. Description of Related Art
Infrared communications circuitry which includes infrared transceivers and transmitters is integrated into a variety of battery operated devices ranging from computers and personal data assistants, or PDAs, to simple television remote control units. A variety of different types of devices contain infrared communications circuits. These integrated infrared communications circuits either are always on and have no power on/off capability, or are switched on and off either as the devices that incorporate them are switched on and off or independently of the devices that incorporate them but under their control, as with laptop computers and PDAs.
Advantageously, the present invention provides an infrared activated power switch that draws little power in the absence of infrared signal activity and is responsive to infrared signal activity to power up associated electronic circuitry.
One embodiment of the present invention is a battery operated ink capture device for operating in a minimum power dissipation mode in the absence of active use thereof, and in a normal power dissipation mode during active use thereof. The ink capture device comprises a battery voltage terminal; a switched power source having a control input, a power input, and a power output, the power output furnishing a normal operating voltage during the normal power dissipation mode and furnishing effectively a zero voltage during the minimum power dissipation mode; a digitizer having a power input coupled to the power output of the switched power source; a wireless communications port having a received signal output and a first power input, the first power input being coupled to the battery voltage terminal at least during the minimum power dissipation mode; and a communications activity detector having an input coupled to the received signal output of the wireless communications port, an output coupled to the control input of the switched power source, and a power input coupled to the battery voltage terminal at least during the minimum power dissipation mode.
Another embodiment of the present invention is a handwriting capture system operating in a minimum power dissipation mode in the absence of active use thereof, and in a normal power dissipation mode during active use thereof. The handwriting capture system comprises a battery voltage terminal; a switched power source having a control input, a power input, and a power output, the power output furnishing a normal operating voltage during the normal power dissipation mode and furnishing effectively a zero voltage during the minimum power dissipation mode; a digitizer tablet having a power input coupled to the power output of the switched power source and a digital signal output; a first infrared communications transceiver port including a first section having a received signal output and a first power input, and a second section coupled to the digital signal output of the digitizer and having a second power input, the first power input being coupled to the battery voltage terminal at least during the minimum power dissipation mode and the second power input being coupled to the power output of the switched power source; a communications activity detector having an input coupled to the received signal output of the infrared communications transceiver port, an output coupled to the control input of the switched power source, and a power input coupled to the battery voltage terminal at least during the minimum power dissipation mode; and a digital image capture device having a second infrared communications transceiver port, the second communications port being disposed within range of the first communications port.
Yet another embodiment of the present invention is a method of controlling power applied to a handwriting capture system comprising a battery operated ink capture device and a battery operated image capture device having a wireless link therebetween. The method comprises applying power to a subset of circuits in the ink capture device, the subset comprising a wireless receiver in the ink capture device and excluding a digitizing tablet in the ink capture device; communicating an activation signal from the image capture device to the ink capture device; detecting the activation signal in the wireless receiver of the ink capture device; and applying power to the entire ink capture device in response to the detecting step.